Rozprawy doktorskie: „Ultra high vacuum”

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Barreto, Suzana Maria. "Towards autonomous sample positioning for ultra high vacuum chambers". Thesis, Aberystwyth University, 2018. http://hdl.handle.net/2160/77e7f40d-eb63-4062-bc1f-e5e4e7d102a9.

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Materials Science has in recent years become a high priority research area, having been identified as a growth sector for the UK economy over the next decade. Breakthroughs in this field are likely to have a significant impact on every area of our lives. There has recently been a trend toward automation at beamlines which is driven by rapid technology advancement. This technology advancement has improved the quality of experiment data and has allowed data collection times to improve exponentially. The Materials Science Research Group in the Institute of Mathematics, Physics and Computer Science, at Aberystwyth University have achieved international recognition for their research on materials under extreme conditions. They have a rich history in the development and use of specialist instruments to conduct real time surface analysis. Their custom made instrumentation has allowed them to greatly improve experiment throughput. Automation of the group's ultra high vacuum chambers is therefore a further enhancement that is advantageous, important, necessary and inevitable. This thesis presents the research undertaken to study what is required to provide automated sample positioning inside vacuum chambers that are operated under ultra high vacuum conditions, as the first step towards automation. As part of the research, a prototype automated positioning system that employs state of the art model based visual tracking techniques was developed to gain an understanding of the challenges the ultra high vacuum environment presents. Experimentation was carried out to assess the effects of different lighting conditions on tracking, evaluate the tracking library, extract suitable extrinsic parameters for tracker initialisation, and evaluate both monocular and stereo mode tracking. Key findings were that the model based tracking is a suitable approach for an automated positioning system but that performance depends on having suitable port placement for the cameras. Stereo tracking provided the best performance but was still prone to divergence at certain relative positions of the manipulator. On linear runs the average error was 0.06mm. On rotational runs, anti-clockwise runs proved better with an average error of 2^o to 3^o. The high errors of mixed rotational and linear tracking runs did not match the visual outputs indicating that there were inherent errors in the data evaluation. Tracking output video footage is available at [8]. More work is needed to take the system forward and close the tracking loop. Recommendations for improvements were provided.

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Schambach, Philip [Verfasser]. "Tip-enhanced Raman spectroscopy in ultra-high vacuum / Philip Schambach". Berlin : Freie Universität Berlin, 2013. http://d-nb.info/104348079X/34.

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Woodburn, Charles N. "Development of low-temperature, ultra high vacuum, scanning tunnelling microscope". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264506.

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Pires, Ellis John. "Electrical conductivity of single organic molecules in ultra high vacuum". Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/56796/.

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Measurement of the I(V ) characteristics of single molecules is the first step towards the realisation of molecular electronic devices. In this thesis, the electronic transport properties of alkanedithiol (ADT) and alkylthiol-terminated oligothiophene molecules are investigated under ultra high vacuum (UHV) using a scanning tunnelling microscope (STM). Two techniques are employed that rely upon stochastic molecular bridge formation between gold STM tip and substrate; a novel I(V; s) method is proven to be a powerful alternative to the well-known I(s) method. For ADTs, three temperature-independent (180 - 390 K) conduction groups are identified, which arise from different contact-substrate coordination geometries. The anomalous reduction of conductance at small chain lengths reported by other groups for non-UHV conditions is far less pronounced here; all groups closely follow the anticipated exponential decay with chain length, β = (0.80 ± 0.01) Å ¹, until a small deviation occurs for the shortest molecule. Thus, the likely explanation for the anomalous effect is hydration of thiol groups. The I(V ) curves were fitted using a rectangular tunnel barrier model, with parameters in agreement with literature values; m = (0.32 ± 0.02) m, φ = 2 eV. For the oligothiophene molecules, one common temperature-independent (295-390 K) conduction group was identified; the conductance decays exponentially with molecular length, with different factors of β = (0.78 ± 0.15) Å ¹ and β = (0.16 ± 0:04) Å ¹ for length changes to the alkylthiol chains and thiophene backbone, respectively. An indented tunnel barrier model, anticipated from the physical and electronic structure of the molecules, was applied to fit the measured I(V ) curves; φ1 = φ3 = 2 eV, φ2 = 1.3 to 1.6 eV, m = 0.17 to 0.24 m. These UHV measurements provide an important baseline from which to better understand recent reports indicating hydration-dependent, and hydration-induced temperature-dependent, transport properties.

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Baily, Christopher John. "UHV studies of the adsorption of small adsorbate molecules on low index platinum single crystals". Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288413.

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Al-Rawi, S. A. N. "Silicon sublimation at ultra high vacuum with microprocessor monitoring and measurements". Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382189.

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Ebert, Helen Diane. "The study of adsorbed species using electrochemical and ultra high vacuum techniques". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255669.

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Ê¿AzÌ£iÌ„m, MuhÌ£ammad. "Ultra high vacuum-scanning electron microscope studies of Cs/Si(100)-2x1". Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385984.

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Newton, Mark A. "Alloy effects in catalysis : the structure and reactivity of the CuPd[85:15]{110}p(2x1) surface". Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240235.

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Lee, King Hung. "Ellipsometric studies of the nucleation of zinc sulphide films in ultra-high vacuum". Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335519.

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Höfer, Katharina. "All in situ ultra-high vacuum study of Bi2Te3 topological insulator thin films". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-220737.

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The term "topological insulator" (TI) represents a novel class of compounds which are insulating in the bulk, but simultaneously and unavoidably have a metallic surface. The reason for this is the non-trivial band topology, arising from particular band inversions and the spin-orbit interaction, of the bulk. These topologically protected metallic surface states are characterized by massless Dirac dispersion and locked helical spin polarization, leading to forbidden back-scattering with robustness against disorder. Based on the extraordinary features of the topological insulators an abundance of new phenomena and many exciting experiments have been proposed by theoreticians, but still await their experimental verification, not to mention their implementation into applications, e.g. the creation of Majorana fermions, advanced spintronics, or the realization of quantum computers. In this perspective, the 3D TIs Bi2Te3 and Bi2Se3 gained a lot of interest due to their relatively simple electronic band structure, having only a single Dirac cone at the surface. Furthermore, they exhibit an appreciable bulk band gap of up to ~ 0.3 eV, making room temperature applications feasible. Yet, the execution of these proposals remains an enormous experimental challenge. The main obstacle, which thus far hampered the electrical characterization of topological surface states via transport experiments, is the residual extrinsic conductivity arising from the presence of defects and impurities in their bulk, as well as the contamination of the surface due to exposure to air. This thesis is part of the actual effort in improving sample quality to achieve bulk-insulating Bi2Te3 films and study of their electrical properties under controlled conditions. Furthermore, appropriate capping materials preserving the electronic features under ambient atmosphere shall be identified to facilitate more sophisticated ex-situ experiments. Bi2Te3 thin films were fabricated by molecular beam epitaxy (MBE). It could be shown that, by optimizing the growth conditions, it is indeed possible to obtain consistently bulk-insulating and single-domain TI films. Hereby, the key factor is to supply the elements with a Te/Bi ratio of ~8, while achieving a full distillation of the Te, and the usage of substrates with negligible lattice mismatch. The optimal MBE conditions for Bi2Te3 were found in a two-step growth procedure at substrate temperatures of 220°C and 250°C, respectively, and a Bi flux rate of 1 Å/min. Subsequently, the structural characterization by high- and low-energy electron diffraction, photoelectron spectroscopy, and, in particular, the temperature-dependent conductivity measurements were entirely done inside the same ultra-high vacuum (UHV) system, ensuring a reliable record of the intrinsic properties of the topological surface states. Bi2Te3 films with thicknesses ranging from 10 to 50 quintuple layers (QL; 1QL~1 nm) were fabricated to examine, whether the conductivity is solely arising from the surface states. Angle resolved photoemission spectroscopy (ARPES) demonstrates that the chemical potential for all these samples is located well within the bulk band gap, and is only intersected by the topological surface states, displaying the characteristic linear dispersion. A metallic-like temperature dependency of the sheet resistance is observed from the in-situ transport experiments. Upon going from 10 to 50QL the sheet resistance displays a variation by a factor 1.3 at 14K and of 1.5 at room temperature, evidencing that the conductivity is indeed dominated by the surface. Low charge carrier concentrations in the range of 2–4*10^12 cm^−2 with high mobility values up to 4600 cm2/Vs could be achieved. Furthermore, the degradation effect of air exposure on the conductance of the Bi2Te3 films was quantified, emphasizing the necessity to protect the surface from ambient conditions. Since the films behave inert to pure oxygen, water/moisture is the most probable source of degeneration. Moreover, epitaxially grown elemental tellurium was identified as a suitable capping material preserving the properties of the intrinsically insulating Bi2Te3 films and protecting from alterations during air exposure, facilitating well-defined and reliable ex-situ experiments. These findings serve as an ideal platform for further investigations and open the way to prepare devices that can exploit the intrinsic features of the topological surface states
Der Begriff "Topologischer Isolator" (TI) beschreibt eine neuartige Klasse von Verbindungen deren Inneres (engl. Bulk) isolierend ist, dieses Innere aber gleichzeitig und zwangsläufig eine metallisch leitende Oberfläche aufweist. Dies ist begründet in der nicht-trivialen Topologie dieser Materialien, welche durch eine spezielle Invertierung einzelner Bänder in der Bandstruktur und der Spin-Bahn-Kopplung im Materialinneren hervorgerufen ist. Diese topologisch geschützten, metallischen Oberflächenzustände sind gekennzeichnet durch eine masselose Dirac Dispersionsrelation und gekoppelte Helizität der Spinpolarisation, welche die Rückstreuung der Ladungsträger verbietet und somit zur Stabilisierung der Zustände gegenüber Störungen beiträgt. Auf Grundlage dieser außergewöhnlichen Merkmale haben Theoretiker eine Fülle neuer Phänomene und spannender Experimente vorhergesagt. Deren experimentelle Überprüfung steht jedoch noch aus, geschweige denn deren Umsetzung in Anwendungen, wie zum Beispiel die Erzeugung von Majorana Teilchen, fortgeschrittene Spintronik, oder die Realisierung von Quantencomputern. Aufgrund ihrer relativ einfachen Bandstruktur, welche nur einen Dirac-Kegel an der Oberfläche aufweist, haben die 3D TI Bi2Te3 und Bi2Se3 in den letzten Jahren großes Interesse erlangt. Weiterhin besitzen diese Materialien eine merkliche Bandlücke von bis zu ~0,3 eV, welche sogar Anwendungen bei Raumtemperatur ermöglichen könnten. Dennoch ist deren experimentelle Umsetzung nachwievor eine enorme Herausforderung. Das Haupthindernis, welches bis jetzt insbesondere die elektrische Charakterisierung the topologischen Oberflächenzustände behindert hat, ist die zusätzliche Leitfähigkeit des Materialinneren, welche durch Kristalldefekte und Beimischungen, sowie die Verunreinigung der Probenoberfläche durch Luftexposition bedingt wird. Die vorliegende Arbeit liefert einen Beitrag zu aktuellen den Anstrengungen in der Verbesserung der Probenqualität der TI um die Leitfähigkeit des Materialinneren zu unterdrücken, sowie die anschließende Untersuchung der elektrischen Eigenschaften unter kontrollierten Bedingungen durchzuführen. Weiterhin sollen geeignete Deckschichten identifiziert werden, welche die besonderen elektronischen Merkmale der TI nicht beeinflussen sowie diese gegen äußere Einflüsse schützen, und somit die Durchführung anspruchsvoller ex situ Experimente ermöglichen können. Die untersuchten Bi2Te3 Schichten wurden mittels Molekularstrahlepitaxie (MBE) hergestellt. Es konnte gezeigt werden, dass es allein durch Optimierung der Wachstumsbedingungen möglich ist Proben herzustellen, die gleichbleibend isolierende Eigenschaften des TI Inneren aufweisen und Eindomänen-Ausrichtung besitzen. Die zentralen Faktoren sind hierbei die Aufrechterhaltung eines Flussratenverhältnisses von Te/Bi ~8 der einzelnen Elemente, sowie die Wahl einer ausreichend hohen Substrattemperatur, um ein vollständiges Abdampfen (Destillation) des überschüssigen Tellur zu erreichen. Weiterhin müssen Substrate mit gut angepassten Gitterparametern verwendet werden, welches bei BaF2 (111) gegeben ist. Optimales MBE Wachstum konnte durch ein Zwei-Stufen Prozess bei Substrattemperaturen von 220°C und 250°C und einer Bi-Verdampfungsrate von 1 Å/min erreicht werden. Die nachfolgende Charakterisierung der strukturellen Eigenschaften, Photoelektronenspektroskopie, sowie temperaturabhängige Leitfähigkeitsmessungen wurden alle in einem zusammenhängenden Ultrahochvakuum-System durchgeführt. Auf diese Weise wird eine zuverlässige Erfassung der intrinsischen Eigenschaften der TI sichergestellt. Zur Überprüfung, ob die Leitfähigkeit der Proben tatsächlich nur durch die Oberflächenzustände hervorgerufen wird, wurden Filme mit Schichtdicken im Bereich von 10 bis 50 Quintupel-Lagen (QL; 1QL~ 1 nm) hergestellt und charakterisiert. Winkelaufgelöste Photoelektronenspektroskopie (ARPES) belegt, dass das chemische Potential (Fermi-Niveau) in allen Proben innerhalb der Bandlücke der Bandstruktur des Materialinneren liegt und nur von den topologisch geschützten Oberflächenzuständen gekreuzt wird, welche die charakteristische lineare Dirac Dispersionsrelation aufweisen. Die temperaturabhängigen Widerstandsmessungen zeigen ein metallisches Verhalten aller Proben. Bei der Variation der Schichtdicke von 10 zu 50QL wird eine Streuung des Flächenwiderstandes vom Faktor 1,3 bei 14K und 1,5 bei Raumtemperatur beobachtet. Dies beweist, dass die gemessene Leitfähigkeit vorrangig durch die topologisch geschützten Oberflächenzustände hervorgerufen wird. Eine geringe Oberflächenladungsträgerkonzentration im Bereich von 2–4*10^12 cm^−2 und hohe Mobilitätswerte von bis zu 4600 cm2/Vs wurden erreicht. Weiterhin wurden die negativen Auswirkungen auf die Eigenschaften der TI durch Luftexposition quantifiziert, welches die Notwendigkeit belegt, die Oberfläche der TI vor Umgebungseinflüssen zu schützen. Die Proben verhalten sich inert gegenüber reinem Sauerstoff, daher ist Wasser aus der Luftfeuchte höchstwahrscheinlich der Hauptgrund für die beobachtbare Verschlechterung. Darüber hinaus konnte epitaktisch gewachsenes Tellur als geeignete Deckschicht ausfindig gemacht werden, welches die Eigenschaften der Bi2Te3 Filme nicht beeinflusst, sowie gegen Veränderungen durch Luftexposition schützt. Die gewonnenen Erkenntnisse stellen eine ideale Grundlage für weiterführende Untersuchungen dar und ebnen den Weg zur Entwicklung von Bauelementen welche die spezifischen Besonderheiten der topologischen Oberflächenzustände

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Lain, amador Lucia. "Production of ultra-high-vacuum chambers with integrated getter thin-film coatings by electroforming". Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD006/document.

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Des couches minces co-deposées de Titanium Zirconium Vanadium (TiZrV) sont utilisés dans les accélérateurs de particules et les sources de lumière synchrotron pour maintenir les conditions d’ultravide. Elles sont pulvérisés sur les parois internes des chambres à vides, transformant celles-ci en « pompe chimique de gaz ». La tendance dans la conception d’accélérateurs d’électrons consiste à approcher les pôles des aimants de direction au plus près du faisceau d’électrons. Cela implique la réduction du diamètre des tubes hébergeant le vide et nécessite l’utilisation de très petits diamètres pour les chambres à vide. L’application du dépôt par vaporisation physique (PVD) dans un aussi faible diamètre devient alors très difficile. Le but de ce projet est de développer une nouvelle procédure de dépôt couplé à l’assemblage, en utilisant un mandrin sacrificiel en aluminium comme substrat de la couche mince en même temps que la création autour de lui de la chambre à vide elle-même par électroformage de cuivre. La première partie de l’étude concerne la production et la caractérisation de chambre de cuivre électroformées. La robustesse mécanique de l’assemblage complet a été validée, et les caractéristiques du film lui-même sont etudièes par microscopie électronique à balayage (MEB), diffraction des rayons X (DRX), spectrométrie de fluorescence-X (XRF) et spectrométrie de photoélectrons X (XPS). De plus, les performances de « pompage chimique des gaz » des nouvelles chambres à vide ainsi élaborées sont mesurées et comparées avec des valeurs de références de revêtements déposés par des procédures classiques dans des tubes de plus grand diamètres. La deuxième partie de l‘étude concerne l’évaluation des impuretés incluses lors des différentes étapes du procédé : le revêtement PVD, l’électroformage et l’étape de dissolution chimique du mandrin. La spectrométrie de désorption thermique et les profils de composition en épaisseur par XPS permettent de quantifier les impuretés dans le cuivre électroformé et dans le film de TiZrV. De plus, la présence d’hydrogène emprisonné dans le cuivre électroformé est étudiée à partir de différents bains à base de sulfate de cuivre. L’un d’entre eux, sans additifs, nécessite l’utilisation de courants pulsés. Le comportement électrochimique du bain permet la sélection de différents paramètres de séquences de pulses, dérivées de situations typiques des courbes transitoires. Finalement, le développement de prototypes de taille réelle a été atteint avec la création de chambres à vide revêtues de TiZrV de 2 mètres de long et 4mm de diamètre, ce qui n’a pas d’équivalent à ce jour
Titanium Zirconium Vanadium (TiZrV) thin film coatings are used in particle accelerators and synchrotron light sources to maintain ultra-high vacuum conditions. They are deposited on the internal walls of the vacuum chambers, transforming them from a gas source into a chemical pump. The trend in electron accelerators design consists in approaching the poles of the steering magnets close to the electron beam. This implies reducing the bore hosting the vacuum chamber and using very small diameter vacuum pipes. The application of physical vapor deposition (PVD) in such small diameter chambers becomes then very difficult. The aim of this project is to develop a novel procedure of coating/assembly, using a sacriﬁcial aluminium mandrel as substrate of the thin film together with the creation of a surrounding copper chamber by electroforming. The first part of the study deals with the production and characterization of the electroformed chambers. The mechanical robustness of the assembly is checked, and the film characterization is performed by secondary electron microscopy (SEM), X-ray diffraction analysis (XRD), X-ray Fluorescence Spectroscopy (XRF) and X-Ray Photoelectron Spectroscopy (XPS). Moreover, the pumping performance is measured and compared with reference values of coatings produced by the standard PVD technique. The second part of the study evaluates the impurities included during the different steps of the process: PVD coating, electroforming and chemical etching of the mandrel. Thermal desorption spectroscopy and XPS depth profiling allow to quantify the impurities in the electroformed copper and the TiZrV thin film. Furthermore, the presence of hydrogen trapped in the electroformed copper is studied for different copper sulphate baths. One of them, without additives, require the use of pulse currents. The electrochemical behaviour of the bath allows the selection of different pulse parameters, derived from typical situations on the transient curves. Finally, the development of real-scale prototypes was achieved with the creation of a 4 mm diameter, 2 meters TiZrV coated vacuum chamber, which is unrivalled up to date

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Taylor, Martin. "The ultra-selective hydrogenation of furfural on PtCu supported bimetallic nanoparticles and on Pt(111) under ultra-high vacuum". Thesis, Aston University, 2017. http://publications.aston.ac.uk/33308/.

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The selective transformation of furfural, a biomass platform molecule, was studied on Pt based heterogeneous catalysts and model single crystal surfaces. Hydrogenation reactions were carried out at pressures ranging from ultra-high vacuum to 20 bar. Temperature Programmed Desorption data in conjunction with Scanning Tunnelling Microscopy suggest that the decarbonylation of furfural on clean Pt(111) and the hydrogenation of furfural on hydrogen pre-covered Pt(111) is governed by surface crowding, molecular orientation and hydrogen bonding networks of the adsorbed molecules. Liquid phase experimentation on Pt nanoparticles, dispersed on a wide range of oxide supports, show that Pt is a very active hydrogenation catalyst even at very mild temperature and pressure conditions. The reaction was found to be highly dependent on the solvent used, while catalyst support is critical for maintaining thermally stable, monodisperse nanoparticles. The addition of Cu into Pt nanoparticles was investigated in a range of Pt:Cu metal molar ratios varying from pure Pt to pure Cu. This was achieved by using a modified polyol synthesis to generate colloidal nanoparticles, followed by thermal processing. Bimetallic particles synthesized using a sulphur free Cu precursor, were found to be beneficial for the suppression of CO adsorption, normally a poison for this reaction, which is formed from the decarbonylation of furfural. The alloying of these two metals had a profound effect on the overall catalytic activity by providing superior initial rates of reaction and catalytic turnover, as well as achieving high selectivities towards furfuryl alcohol, surpassing the behaviour of pure Pt catalyst across 3 different pressures. Finally, Single Atom Alloys (SAA), formed via the galvanic replacement of dispersed host Cu nanoparticles by Pt was investigated. Pt:Cu nanoparticles with atomic ratios ranging from 1:20 to 0.5:250 were synthesized and tested. After overcoming a brief induction period due to the reduction of surface CuO and possibly the reordering of the surface atoms, SAAs exhibit extremely high rates of hydrogenation, surpassing the catalytic turnover for monometallic and bimetallic catalysts. These cutting edge materials are at the frontier of catalyst research, proving to be ideal materials for the future of green chemistry due to both their activity and economic viability.

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Gedik, Abdullah. "Energy threshold for laser induced breakdown on a metal surface under high and ultra high vacuum conditions". Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28165.

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Hamann, Christian [Verfasser]. "An Electrospray Ion Source for Ultra-High Vacuum Deposition of Organic Molecules / Christian Hamann". Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/104859226X/34.

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Fostner, Shawn. "Ultra high vacuum fabrication of metallic contacts for molecular devices on an insulating surface". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95011.

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The preparation and characterization of metallic wires on insulating substrates by a variety of mechanisms has been explored. A multi-scale approach utilizing microfabricated silicon stencil masks, feedback controlled electromigration, and field induced metal cluster deposition in a novel geometry has been explored on potassium bromide (KBr), indium phosphide (InP), and silicon oxide substrates in an ultra-high vacuum environment (UHV). The initial deposition of gold, and tantalum wires between one hundred nanometers and micrometers in size was performed using reinforced silicon nanostencils. The stencil fabrication was discussed, and an examination of the deformation of the integrated structures under the deposition of highly stressed tantalum films was shown to be significantly smaller than typical structures. Metallic wires deposited using these stencils as well as electron beam lithography were electrically stressed and the breaking characteristics analyzed. Typical nanometer scale gaps were observed, as well as larger features more commonly found in the breaking of bamboo-like structures in gold wires 100 nm in size or less, particularly with a significant series resistance. These larger gaps are expected to be more applicable for the deposition of subsequent metallic clusters and preparation of molecular devices. As a step towards connecting the initially deposited wires as well as localized molecules in an a fashion allowing atomic scale imaging by AFM, modelling and experiments of field induced deposition of gold clusters on KBr and InP substrates was carried out. Deposition on InP substrates with a backside 2D electron gas as a counter-electrode demonstrated the feability of this deposition technique in UHV. Subsequent depositions on or adjacent to metallic pads on the bulk insulating KBr provided a proof of principle of the technique, though some experimental limitations such as large current pulses with the tip in close proximity to the surface are d
La préparation et la caractérisation de fils métalliques sur des substrats isolants par une variété de mécanismes a été explorée. Une approche multi-échelle utilisant des masques-stencils microfabriqués de silicium, l'électromigration contrôlée par rétroaction, et le dépôt induit par champ en nouvelle géométrie d'agrégats métalliques, a été explorée sur des substrats de bromure de potassium (KBr), de phosphure d'indium (InP) et d'oxyde de silicium sous Ultra Haut Vide (UHV). Le dépôt initial de fils d'or et de tantale entre cent nanomètres et quelques micromètres a été réalisé en utilisant des nanostencils au silicium renforcé. La fabrication des stencils a été discutée, et un examen de la déformation des structures intégrées dans le cas du dépôt de couches de tantale sous hautes contraintes a montré qu'elle était significativement plus petite que pour les structures typiques. Les fils métalliques déposés à l'aide de ces stencils, ainsi que la lithographie par faisceau électronique ont été mis sous contrainte électriquement et les caractéristiques de rupture analysées. Des vides typiques à l'échelle du nanomètre ont été observés, ainsi que des structures communément retrouvées dans la rupture de structure de type bambou dans les fils d'or de 100nm et moins, en particulier avec une résistance en série importante. Ces vides plus grands devraient être plus applicables pour le dépôt par la suite d'agrégats métalliques et la préparation de dispositifs moléculaires. Une étape a été franchie vers la connexion des fils déposés initialement ainsi que de molécules localisées de façon imageable, en réalisant un modèle et des expériences de dépôt induit par champ d'agrégats d'or sur KBr et InP. Le dépôt sur des substrats InP avec derrière un gaz d'électrons 2D comme contre-électrode a démontré la faisabilité de cette technique de dépôt sous UHV. Des dépôts ultérieurs sur ou

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Manzoor, Tahir. "Ellipsometric studies of the nucleation and growth of thin films in ultra high vacuum". Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335428.

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Luhman, Xavier D. "Sulfurizing and selenizing metal films in ultra-high vacuum by hydride gas kinetic control". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122393.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (page 30).
Molecular beam epitaxy (MBE) is an important, well-established method for creation of thin films. The addition of gaseous sources of hydrogen sulfide and hydrogen selenide is not currently a well-documented or common modification to such systems. While the thermodynamics of using such sources for the production of various chalcogenide thin films are favorable, the actual results thus far do not demonstrate the desired outcome. This indicates that the kinetics of the desired reactions are inhibiting the process. Compared to oxygen, reactions involving sulfur and selenium are slow. In order to ensure that the hydride gases have the opportunity to react as desired, it is necessary to keep the system free of oxygen and to maximize the collisions of gas molecules with the substrate. The first requirement should be achieved simply by using MBE for the process. The second requirement is not provided for in a typical MBE system. Thus, modifications are necessary to increase the reaction rate of the gases, namely by extending the source lines to be closer to the substrate. This thesis addresses the design process for tubing inserts in an existing MBE system.
by Xavier D. Luhman.
S.B.
S.B. Massachusetts Institute of Technology, Department of Materials Science and Engineering

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Lautenschlager, Eric J. "Silicon nanoclusters : ultra high vacuum laser ablation fabrication and in situ scanning tunneling microscopy characterization /". Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.

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Day, Brian Scott. "The Dynamics of Gas-Surface Energy Transfer in Collisions of Rare Gases with Organic Thin Films". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29860.

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Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools. There are many questions regarding the dynamic details that occur during the interaction time between gas molecules and organic surfaces. For example, how does interfacial structure and density affect energy transfer? What roles do intramonolayer forces and chemical identity play in the dynamics? We have approached these questions by scattering high-energy, rare gas atoms from functionalized self-assembled monolayers. We used classical trajectory simulations to investigate the atomic-level details of the scattering dynamics. We find that approximately six to ten carbon atoms are involved in impulsive collision events, which is dependent on the packing density of the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less energy is transferred to the surface on average and the less often the incident atoms come into thermal equilibrium with the surface. In addition to the purely hydrocarbon monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid collision partners than surfaces with smaller inter-chain forces, such as van der Waals forces. Finally, we find some interesting properties for organic surfaces that possess fluorinated groups. For argon scattering, energy transfer decreases with an increasing amount of surface fluorination, whereas krypton and xenon scattering transfer most energy to monolayers terminated in CF3 groups, followed by purely hydrocarbon surfaces, and then perfluorinated surfaces.
Ph. D.

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Morse, Michael Ty. "Growth of erbium-doped Si/SiGe double heterostructures by ultra-high vacuum chemical vapor deposition". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10380.

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Stojilovic, Nenad. "Interaction of gases with Zr(0001) and Zircaloy-4 surfaces under ultra-high vacuum conditions". University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1132677151.

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Magnano, Graziano. "Elestrospray deposition in ultra-high vacuum : the development of a deposition system for non-volatile molecules". Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546586.

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KURIMOTO, Shinji, Kenji HIROTA, Daisuke TOKUMOTO i Toshihiko MORI. "Improving High Precision and Continuous Process of Ultra-Fine Piercing by SiC Fiber Punch". The Japan Society of Mechanical Engineers, 2004. http://hdl.handle.net/2237/9036.

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Haglund, Adam. "Reduction of hydrogen embrittlement on Electrogalvanized Ultra High Strength Steels". Thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-236603.

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Ultra-high strength steels is known to be susceptible for hydrogen embrittlement at very low concentrations of hydrogen. In this thesis three methods to prevent or reduce the hydrogen embrittlement in martensitic steel, with tensile strength of 1500 MPa, were studied. First, a barrier layer of aluminium designed to prevent hydrogen to enter the steel, which were deposited by vacuum evaporation. Second, a decarburization process of the steels surface designed to mitigate the induced stresses from cutting. Last, a hydrogen relief treatment at 150°C for 11 days and 200°C for 4 days, to reduce the hydrogen concentration in the steel. The effect of the hydrogen embrittlement was analyzed by manual measurements of the elongations after a slow strain rate testing at 5*10-6 mm/s, and the time to fracture in an in-situ constant load test with a current density of 1.92 mA/cm2 in a 0.5 M Na2SO4 solution. The barrier layer showed an increase in time to fracture, but also a decrease in elongations. The decarburized steel had a small increase in the time to fracture, but not enough to make it a feasible process. The hydrogen relief treatment showed a general decrease in hydrogen concentrations, but the elongation measurements was irregular although with a tendency for improvement. The simplicity of the hydrogen relief treatment makes it an interesting process to reduce the influence of hydrogen embrittlement. However, more investigations are necessary.

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Weiss, Christian [Verfasser]. "STM beyond vacuum tunnelling : scanning tunnelling hydrogen microscopy as a route to ultra-high resolution / Christian Weiss". Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1028003706/34.

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Cooper, Kevin W. "Characterization of Diamond Like Carbon Thin Films Fabricated by Unbalanced Magnetron Sputtering under Ultra-High Vacuum Conditions". Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1373458861.

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Clark, Kendal. "Ultra High Vacuum Low Temperature Scanning Tunneling Microscope for Single Atom Manipulation on Molecular Beam Epitaxy Grown Samples". Ohio University / OhioLINK, 2005. http://www.ohiolink.edu/etd/view.cgi?ohiou1125611713.

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Tekiel, Antoni. "Ultra-high vacuum fabrication of nanoscale systems for studying single-electron charging by room-temperature atomic force microscopy". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119570.

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In this work we describe ultra-high vacuum fabrication of a nanoscale system that reveals Coulomb blockade at room temperature and its characterization by single-electron sensitive electrostatic force microscopy (e-EFM). The system consists of Au nanoparticles separated from an Fe(001) back electrode by a crystalline ultra-thin NaCl film. Due to the small size of the nanoparticles (3.5 nm high), the Coulomb blockade can be observed at room temperature. An atomic force microscopy (AFM) cantilever is used as a movable gate to charge individual nanoparticles via single-electron tunneling from the back electrode. At the same time the tunneling is detected by measuring frequency shift and damping of the oscillating cantilever. The e-EFM technique can overcome limitations of other characterization methods based on lithographic fabrication. So far, however, it has been successfully used only at low-temperatures. In this work, we extend the e-EFM technique to room temperature by carefully tuning the sample design and fabrication relative to the cantilever response to achieve maximum sensitivity. To grow atomically defined tunnel barriers we investigate the morphology of MgO and NaCl ultra-thin films on Fe(001) surfaces by non-contact-AFM and low energy electron diffraction (LEED). First, we demonstrate that the quality of MgO films, typically grown in ultra-high vacuum (UHV) by electron-beam evaporation, can be improved by using reactive deposition method that gives full control over the gaseous species existing in the evaporated beam. Second, we investigate the effects of temperature and oxygen presence on the growth of NaCl on Fe(001). As a result, we develop a protocol to grow NaCl films on the Fe(001)-p(1x1)O surface in a layer-by-layer mode, yielding atomically flat films with 40-60 nm wide terraces (on a 12 ML thick film) and with far fewer defects than the MgO films. Using the NaCl film as a tunnel barrier that can be easily adjusted by modifying the film thickness we characterize single-electron charging at room temperature of individual Au nanoparticles formed after thermal evaporation onto a 6 monolayer thick NaCl film. We demonstrate how a combination of e-EFM and finite element electrostatic simulation can be used for revealing electronic and morphological properties of individual Au nanoparticles. As a result, the electron addition energy, the capacitance, tunneling rates and an approximated shape of an individual nanoparticle have been determined. Numerical simulations point towards a total capacitance dominated by the mutual capacitance between the nanoparticle and the back electrode. A comparison with the experimental value, determined from measurement of the addition energy, indicates that the nanoparticles should be modeled as truncated spheres in order to reduce the mutual capacitance to the substrate. This observation has a fundamental impact on the design of nanoelectronic circuits, where the components have to meet desired requirements for capacitances that determine coupling and charging effects. The fabrication flexibility and the fact that all measurements were performed in-situ on samples prepared under ultra-clean conditions make the presented system attractive for further studies. In particular, this approach can be used to study quantum mechanically coupled quantum dots and the catalytic activity of Au nanoclusters at room temperature.
Dans ce travail, nous décrivons la fabrication sous ultra haut vide (UHV) d'un système à l'échelle nanométrique qui révèle le blocage de Coulomb à température de la pièce, ainsi que sa caractérisation par microscopie à force électrostatique sensible à un électron (single-electron sensitive electrostatic force microscopy, e-EFM). Le système est constitué de nanoparticules d'or séparées d'une électrode de Fe(001) par un film cristallin ultra mince de NaCl. Dû à la petite taille des nanoparticules (3.5 nm maximum), le blocage de Coulomb est observable à température ambiante. Un cantilever de microscope à force atomique (MFA) est utilisé comme une grille électrique déplaçable pour charger individuellement les nanoparticules par le passage de charge élémentaire par effet tunnel à partir de l'électrode. Ce passage d'électron est détecté en mesurant simultanément le changement de fréquence de résonance, ainsi que l'amortissement de l'oscillation du cantilever. La technique e-EFM permet de contourner certaines limitations inhérentes aux techniques de caractérisation basées sur la fabrication par lithographie. Toutefois, cette technique a été appliquée avec succès seulement à basses températures. Dans ce travail, nous étendons la technique e-EFM à température ambiante par un ajustement minutieux du design de l'échantillon et de sa fabrication en fonction de la réponse du cantilever de sorte à maximiser la sensibilité de la mesure. Pour croître une jonction tunnel définie à l'échelle atomique, nous étudions la morphologie de couches minces de MgO et de NaCl sur une surface de Fe(001) par microscopie à force atomique non-contact et par diffraction d'électrons lents (Low Energy Electrons Diffraction, LEED). Premièrement, nous démontrons que la qualité des couches minces de MgO, typiquement crûes sous UHV par évaporation sous faisceau d'électrons (electron-beam evaporation), peut être améliorée par l'utilisation d'une méthode de déposition réactive qui donne un contrôle total sur les espèces gazeuses présentes dans le faisceau d'évaporation. Deuxièmement, nous étudions l'effet de la température et de la présence d'oxygène sur la croissance du NaCl sur une surface de Fe(001). Conséquemment, un protocole pour la croissance de films de NaCl sur une surface de Fe(001)-p(1x1)O déposés couche par couche. Ces films plats à l'échelle atomique présentent des terrasses de 40-60 nm de large et contiennent beaucoup moins de défauts cristallins que les films de MgO.En utilisant ces couches minces de NaCl comme jonction tunnel facilement ajustables par une modification de leur épaisseur, nous caractérisons le chargement d'électron à température ambiante de nanoparticules individuelles formées par évaporation thermique sur un film de 6 monocouches de NaCl. Nous montrons comment la combinaison de la technique e-EFM et de simulations électrostatiques par éléments finis peut être utilisée pour révéler les propriétés électroniques et morphologiques de nanoparticules d'or individuelles. Ainsi, l'énergie de chargement, la capacitance, la fréquence de passage par effet tunnel et la forme approximative des nanoparticules ont été déterminées. Des simulations numériques montrent que la capacitance totale est dominée par la capacitance mutuelle entre la nanoparticule et l'électrode. En comparant avec les valeurs expérimentales, déterminées par une mesure de l'énergie de chargement, on montre que les nanoparticules devraient être modélisées par des sphères tronquées pour réduire la capacitance mutuelle avec le substrat. Cette observation a un impact fondamental pour le design de circuits nanoélectroniques dans lesquels les composantes doivent avoir des capacitances définies, étant donné que celles-ci déterminent les effets de couplage et de chargement.La flexibilité de la technique de fabrication et le fait que toutes les mesures ont été effectuées in situ sur des échantillons dans des conditions ultra propres rendent le système attrayant pour de futures études.

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Roos, Mathias. "Emissão de eletrons por efeito de campo em diamante policristalino dopado com boro e desenvolvimento de um novo sistema de ultra alvo vacuo". [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259948.

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Orientador: Vitor Baranauskas
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-11T10:03:42Z (GMT). No. of bitstreams: 1 Roos_Mathias_M.pdf: 4816472 bytes, checksum: 51a357faa29ccbd01723b1d6ca5abf27 (MD5) Previous issue date: 2007
Resumo: Na primeira parte deste trabalho amostras de diamante poli-cristalino dopado com boro foram crescidas por deposição química a vapor assistida por filamento quente. As características de emissão de campo foram investigadas. A dopagem (NB) em amostras diferentes foi variada pelo controle da concentração B/C no fluxo de gases durante o processo de crescimento. Os campos limiares (Eth) para emissão de campo foram medidos e relacionados com as concentrações B/C usadas. Assim, a influência das bordas entre os grãos, a dopagem e a morfologia da superfície na emissão de campo foram investigadas. A saturação da dopagem foi observada para altas concentrações B/C. O transporte de cargas através das bordas entre os grãos e as propriedades locais de emissão na superfície foram modeladas por dois mecanismos que afetam a emissão de campo. Correntes de emissão de 500 nA·cm-2 foram obtidas para campos elétricos de 8 V·µm-1. Na segunda parte desta tese, a construção de um novo sistema de ultra alto vácuo (UHV) para realizar medições de emissão de campo é descrita. A construção inclui o projeto integral de uma câmara de UHV com sistema de bombas, conjunto de manipuladores, suportes mecânicos e a infraestrutura do laboratório
Abstract: In the first part of this thesis, the study of field emission properties of hot filament chemical vapor deposited boron doped polycrystalline diamond is described. The doping level (NB) of different samples was varied controlling the B/C concentration in the gas feed during the growth processes. The threshold field (Eth) for electron emission in dependence on different B/C concentrations was measured and the influence of grain boundaries, doping level and surface morphology on the field emission properties was investigated. For high B/C ratios doping saturation was observed. Carrier transport through conductive grains and local emission properties of surface sites figured out to be two independent limiting effects on field emission. Emitter currents of 500 nA·cm-2 were obtained using electric fields less than 8 V·µm-1. In the second part the construction of a new UHV system for field emission measurements is described, including the complete project of a UHV chamber with pump system, manipulators and sample transfer system, mechanical supports and the infrastructural requirements of the laboratory
Mestrado
Eletrônica, Microeletrônica e Optoeletrônica
Mestre em Engenharia Elétrica

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Cao, Yuan. "Thin Cr2O3 (0001) Films and Co (0001) Films Fabrication for Spintronics". Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc822733/.

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The growth of Co (0001) films and Cr2O3 (0001)/Co (0001) has been investigated using surface analysis methods. Such films are of potential importance for a variety of spintronics applications. Co films were directly deposited on commercial Al2O3 (0001) substrates by magnetron sputter deposition or by molecular beam epitaxy (MBE), with thicknesses of ~1000Å or 30Å, respectively. Low Energy Electron Diffraction (LEED) shows hexagonal (1x1) pattern for expected epitaxial films grown at 800 K to ensure the hexagonally close-packed structure. X-ray photoemission spectroscopy (XPS) indicates the metallic cobalt binding energy for Co (2p3/2) peak, which is at 778.1eV. Atomic force microscopy (AFM) indicates the root mean square (rms) roughness of Co films has been dramatically reduced from 10 nm to 0.6 nm by optimization of experiment parameters, especially Ar pressure during plasma deposition. Ultrathin Cr2O3 films (10 to 25 Å) have been successfully fabricated on 1000Å Co (0001) films by MBE. LEED data indicate Cr2O3 has C6v symmetry and bifurcated spots from Co to Cr2O3 with Cr2O3 thickness less than 6 Å. XPS indicates the binding energy of Cr 2p(3/2) is at 576.6eV which is metallic oxide peak. XPS also shows the growth of Cr2O3 on Co (0001) form a thin Cobalt oxide interface, which is stable after exposure to ambient and 1000K UHV anneal.

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Wang, Guanyu. "The Dynamics of Gas-Surface Energy Transfer in Collisions of Diatomic Gases with Organic Surfaces". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51179.

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Understanding interfacial interactions at the molecular level is important for interpreting and predicting the dynamics and mechanisms of all chemistry processes. A thorough understanding of the interaction dynamics and energy transfer between gas molecules and surfaces is essential for the study of various chemical reactions. The collisions of diatomic molecules on organic surfaces are crucial to the study of atmospheric chemistry. Molecular beam scattering experiments performed in ultra-high vacuum chambers provide insight into the dynamics of gas-surface interactions. Many questions remain to be answered in the study of gas-surface interfacial chemistry. For example, what affects the energy transfer between gas molecules and surfaces? How do intermolecular forces affect the interfacial interaction dynamics? We have approached these questions by scattering diatomic gas molecules from functionalized self-assembled monolayers (SAMs). Our results indicate that the intermolecular forces between gas molecules and surfaces play an important role in the energy transfer processes. Moreover, the stronger the intermolecular forces, the more often the incident molecules come into thermal equilibrium with the surface. Furthermore, most of the previous approaches toward understanding gas-surface interaction dynamics considered the interactions as independent incidents. By scattering O2, N2, CO and NO on both CH3- and OH- terminated SAM, we found a correlation between the gas-surface interactions and a bulk property, solubility. Both being strongly affected by intermolecular forces, the gas-surface energy transfer and solubility of gases in surface-similar solvents (water for OH-SAM, n-hexane for CH3-SAM) have a positive correlation. This correlation facilitates the understanding of interfacial dynamics at the molecular level, and helps predict the outcome of the similar-size gas collisions on surfaces.
Master of Science

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Colazzo, Luciano. "On-Surface Supramolecular Networks: Structure and Dynamics of Formation in Ultra-High Vacuum and at the Solid/Liquid Interface". Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3422397.

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On-surface supramolecular chemistry inspired the fabrication of a large variety of atomically controlled systems and on-surface synthesis allowed the production of low-dimensional materials with atomic precision. Since numerous surface-supported nanostructures are constantly developed, their possible applications stimulate diverse areas of research such as catalysis, organic electronics, surface sensing, surface functionalization and nanopatterning. Several protocols and interfacial approaches have been developed for the production of surface-supported supramolecular networks by self-assembly and by far, the increasing interest for nanomaterials with innovative functionalities has boosted the search in on-surface activation of chemical reaction for the covalent stabilization of more complex molecular architectures. Photochemistry was furthered as a promising approach for this purpose and pioneering examples allowed a deeper understanding of light-induced on-surface chemical reactions. However, the search in this field is still at its birth and further research is required. The Scanning Tunneling Microscope provides the necessary resolution for this studies in various conditions, including solid/liquid or solid/air interfaces or Ultra High Vacuum (UHV).
La chimica supra-molecolare di superficie ha permesso la produzione di numerose nanostrutture tramite l'utilizzo di protocolli di sintesi innovativi. In questo modo si sono ottenuti, tramite controllo strutturale a livello atomico e molecolare, numerosi materiali a ridotta dimensionalità. L'applicazione di tali scoperte si sviluppa nell'ambito della ricerca relativa alla catalisi, all'elettronica organica, alla funzionalizzazione e alla sensibilizzazione della superfici. Poiché esistono diversi approcci per per la produzione di tali strutture, la ricerca ha spinto i propri interessi verso la nano-fabbricazione di materiali per ottenerne, sfruttando varie tecniche, di innovativi, più stabili ed efficienti. La fotochimica di superficie in questo senso, permette di ottenere materiali molto complessi ed inoltre permette di capire i fenomeni alla base dei processi di sintesi indotta dalla luce, che ad oggi, non sono del tutto semplici da interpretare. La microscopia a scansione di tunneling (STM) fornisce l'opportuna risoluzione spaziale per questo tipo di studi, i cui principi sono ancora oggi oggetto di dibattito.

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Zhang, Yafen. "Ultrahigh Vacuum Studies of the Reaction Kinetics and Mechanisms of Nitrate Radical with Model Organic Surfaces". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/78003.

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Detailed understanding of the kinetics and mechanisms of heterogeneous reactions between gas-phase nitrate radicals, a key nighttime atmospheric oxidant, and organic particles will enable scientists to predict the fate and lifetime of the particles in the atmosphere. In an effort to acquire knowledge of interfacial reactions of nitrate radical with organics, model surfaces are created by the spontaneous adsorption of methyl-/vinyl-/hydroxyl-terminated alkanethiols on to a polycrystalline gold substrate. The self-assembled monolayers provide a well-defined surface with the desired functional group (-CH3, H2C=CH-, or HO-) positioned precisely at the gas-surface interface. The experimental approach employs in situ reflection-absorption infrared spectroscopy (RAIRS) to monitor bond rupture and formation while a well-characterized flux of NO3 impinges on the organic surface. Overall, the reaction kinetics and mechanisms were found to depend on the terminal functional group of the SAM and incident energy of the nitrate radical (NO3). For reactions of the H2C=CH-SAM with NO3, the surface reaction kinetics obtained from RAIRS reveals that the consumption rate of the terminal vinyl groups is nearly identical to the formation rate of a surface-bound nitrate species and implies that the mechanism is one of direct addition to the vinyl group rather than hydrogen abstraction. Upon nitrate radical collisions with the surface, the initial reaction probability for consumption of carbon-carbon double bonds was determined to be (2.3 ± 0.5) -- 10-3. Studies of reactions of HO-SAM with the effusive source of NO3 suggest that the reaction between NO3 and the HO-SAM is initiated by hydrogen abstraction at the terminal - 'CH2OH groups with the initial reaction probability of (6 ± 1)-- 10-3. An Arrhenius plot was obtained to measure the activation energy of the H abstraction from the HO-SAM. Further, for reactions of the HO-SAM with the high incident energy of NO3 molecules created by molecular beam, the reaction probability for H abstraction at the hydroxyl terminus was determined to be ~0.4. The significant increase in the reaction probability was attributed to the promotion in the ability of NO3 abstracting hydrogen atom at the methylene groups along hydrocarbon chains. The reaction rates of NO3 with the model organic surfaces that have been investigated are orders of magnitude greater than the rate of ozone reactions on the same surfaces which suggests that oxidation of surface-bound organics by nighttime nitrate radicals may play an important role in atmospheric chemistry despite their relative low concentration. X-ray photoelectron spectroscopy (XPS) data suggests that oxidation of the model organic surfaces by NO3 leads to the production of organic nitrates, which are stable for a period time. In addition, the effect of background gases on reactions of NO3 with model organic surfaces needs further investigations at atmospheric pressures. The results presented in this thesis should help researchers to predict the fate and environmental impacts of organic particulates with which nitrate radicals interact.
Ph. D.

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Alves, Otavio Brandão. "Estudo da eletrooxidação de monóxido de carbono em RuO2(110), e visualização morfológica e atômica de fases ricas em oxigênio na oxidação de Ru(0001) através da microscopia de varredura por tunelamento". Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25102007-144021/.

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Nos últimos 30 anos o crescimento paralelo das Ciências de Superfície tradicionais, em ambiente de ultra-alto vácuo (UHV), com a Eletroquímica levou ao nascimento de um novo campo interdisciplinar: Física de Superfície e Eletroquímica. Técnicas de ambas as áreas dão informações complementares e assim, quando realizadas em conjunto podem fornecer muitas respostas em nível atômico, estrutural e eletrônico quando o eletrodo está em contato com a solução eletrolítica. A intenção primordial dessa Dissertação foi o estudo fundamental das fases ricas em oxigênio presentes na superfície de Ru(0001) através de caracterizações eletroquímicas e morfológicas utilizando um sistema que permitiu o acoplamento de uma célula eletroquímica miniatura de fluxo a câmaras de UHV. Inicialmente exibi-se a modificação e a construção de equipamentos necessários para a preparação do sistema binário Au-Pt(111) e do óxido monocristalino Ru2O(110). Imagens de STM em escala morfológica mostraram o crescimento anisotrópico do filme de RuO2(110) sobre um substrato monocristalino de Ru(0001). Resultados obtidos através da técnica de Voltametria Cíclica na eletrooxidação de CO em RuO2(110) corroboraram cálculos teóricos sobre a estrutura da superfície quando esta em ambiente úmido. Superfícies modelos baseadas em ouro, crescido epitaxialmente sobre um substrato de Pt(111), foram preparadas no sistema de UHV. Dados eletroquímicos foram correlacionados às composições superficiais destas, mostrando o efeito do substrato prevalecendo sobre o efeito eletrônico.
In the last 30 years the parallel growth of the traditional Surface Science, under UHV environment, and Electrochemistry gave rise to a new interdisciplinary field: Surface Science and Electrochemistry. Techniques from both sciences give complementary information. Thus, in tandem, they are able to elucidate many atomic, structural and electronic phenomena, of an electrode in contact with a solution. The main goal of this Dissertation was the fundamental study of the Oxygen-rich Ru(0001) surface through electrochemical and morphologic characterizations using a coupled system which allowed the attachment of a miniature flow cell to UVH-chambers. Initially it is shown the construction and modifications of required equipments for the preparation of the binary system Au-Pt(111) and single crystal RuO2(110) oxide. Attainable morphological STM images demonstrated the anisotropic growth of the RuO2(110) over a Ru(0001) substrate. Results of the electrooxidation of CO on RuO2(110), obtained by means of Cyclic Voltammetry, corroborated theoretical calculations concerning the oxide superficial structure in a humid environment. Model surfaces based on Au, epitaxialy grown on a Pt(111) substrate, were prepared under UHV conditions. Electrochemical data and superficial composition were correlated, confirming that the substrate effect overcomes electronic strain effects.

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Hackley, Jason. "A Liquid-Helium-Free High-Stability Cryogenic Scanning Tunneling Microscope for Atomic-Scale Spectroscopy". Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19211.

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This dissertation provides a brief introduction into scanning tunneling microscopy, and then Chapter III reports on the design and operation of a cryogenic ultra-high vacuum scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Other performance characteristics such as thermal drift analysis and a cool-down analysis are reported. Scanning tunneling spectroscopy (STS) measurements based on the lock-in technique were also carried out and showed no detectable presence of noise from the CCC. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic-scale. A study of electron transport in single-walled carbon nanotubes (SWCNTs) was also conducted. In Chapter IV, STS is used to study the quantum-confined electronic states in SWCNTs deposited on the Au(111) surface. The STS spectra show the vibrational overtones which suggest rippling distortion and dimerization of carbon atoms on the SWCNT surface. This study experimentally connects the properties of well-defined localized electronic states to the properties of their associated vibronic states. In Chapter V, a study of PbS nanocrystals was conducted to study the effect of localized sub-bandgap states associated with surface imperfections. A correlation between their properties and the atomic-scale structure of chemical imperfections responsible for their appearance was established to understand the nature of such surface states. This dissertation includes both previously published/unpublished and co-authored material.

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Lin, Tien-Chih 1966. "Interactions of Clean and Sulfur-modified Reactive Metal Surfaces with Aqueous Vapor and Liquid Environments : A Combined Ultra-high Vacuum/electrochemistry Study". Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc278914/.

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The focus of this research is to explore the molecular-level interactions between reactive metal surfaces and aqueous environments by combined ultra-high vacuum/electrochemistry (UHV-EC) methodology. The objectives of this work are to understand (1) the effects of sulfate ions on the passivity of metal oxide/hydroxide surface layer, (2) the effects of sulfur-modification on the evolution of metal oxide/hydroxide surface layer, and (3) the effects of sulfur adsorbate on cation adsorption at metal surfaces.

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Schäfer-Nolte, Eike Oliver [Verfasser], i Jörg [Akademischer Betreuer] Wrachtrup. "Development of a diamond-based scanning probe spin sensor operating at low temperature in ultra high vacuum / Eike Oliver Schäfer-Nolte. Betreuer: Jörg Wrachtrup". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1052894151/34.

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Wilson, Karen E. "Investigations into the role of α-amino acids as chiral modifiers for Ni-based enantioselective heterogeneous hydrogenation catalysts". Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/3108.

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The hydrogenation of β-ketoesters over chirally modified Ni catalysts is a celebrated and thoroughly researched example of an enantioselective heterogeneous catalytic reaction. Enantioselective heterogeneous processes, although extremely attractive in terms of fewer complications in the separation of products from the catalyst, are hindered in their viability as industrial applications due to the lack of detailed knowledge on how chirality is conferred to the metal surface. Surface science techniques have afforded substantial progress into determining mechanisms between modifier, reactant and catalyst to explain the source of enantioselectivity of the system. In this study, a combination of solution and ultra-high vacuum (UHV)-based experiments allow a more realistic interpretation of the surface chemistry underpinning the catalytic reaction as the key step in achieving enantioselective performance is the adsorption of chiral modifiers from solution. The behaviour of (S)-aspartic acid and (S)-lysine on Ni{111} and their interaction with the prochiral β-ketoester methylacetoacetate is investigated in this study to understand their potential as chiral modifiers for the system. In UHV, scanning tunnelling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and temperature programmed desorption (TPD) are used to analyse the conformation and order of the amino acids on the metal, and their thermal stability. Additionally, liquid-solid interface RAIRS and X-ray photoelectron spectroscopy (XPS) are used to examine the modified Ni surface, prepared under aqueous conditions, to give an accurate representation of the catalytic studies. It has been found highly likely that, for (S)-aspartic acid modified Ni{111}, enantioselective sites exist at step or step/kink defects, formed by corrosive leaching of the Ni substrate. Conversely, lysine appears to bind with a high sticking probability to Ni, in the form of lysine islands, and does not appear to etch the Ni chirally. Finally, similar experiments have been carried out on Au{111}, where lysine was found to chiral restructure the surface and form nanofingers, and 2D Ni clusters grown on Au{111} in order to investigate the formation of possible metal-organic frameworks.

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40

Wang, Guanyu. "Interfacial Energy Transfer in Small Hydrocarbon Collisions with Organic Surfaces and the Decomposition of Chemical Warfare Agent Simulants within Metal-Organic Frameworks". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100746.

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A molecular-level understanding of gas-surface energy exchange and reaction mechanisms will aid in the prediction of the environmental fate of pollutants and enable advances toward catalysts for the decomposition of toxic compounds. To this end, molecular beam scattering experiments performed in an ultra-high vacuum environment have provided key insights into the initial collision and outcome of critical interfacial processes on model systems. Results from these surface science experiments show that, upon gas-surface collisions, energy transfer depends, in subtle ways, on both the properties of the gas molecules and surfaces. Specifically, model organic surfaces, comprised of long-chain methyl- and hydroxyl-terminated self-assembled monolayers (SAMs) have been employed to test how an interfacial hydrogen bonding network may affect the ability of a gas-phase compound to thermally accommodate (typically, the first step in a reaction) with the surfaces. Results indeed show that small organic compounds transfer less energy to the interconnected hydroxyl-terminated SAM (OH-SAM) than to the organic surface with methyl groups at the interface. However, the dynamics also appear to depend on the polarizability of the impinging gas-phase molecule. The π electrons in the double bond of ethene (C2H4) and the triple bond in ethyne (C2H2) appear to act as hydrogen bond acceptors when the molecules collide with the OH-SAM. The molecular beam scattering studies have demonstrated that these weak attractive forces facilitate energy transfer. A positive correlation between energy transfer and solubilities for analogous solute-solvent combinations was observed for the CH3-SAM (TD fractions: C2H6 > C2H4 > C2H2), but not for the OH-SAM (TD fractions: C2H6 > C2H2 > C2H4). The extent of energy transfer between ethane, ethene, and ethyne and the CH3-SAM appears to be determined by the degrees of freedom or rigidity of the impinging compound, while gas-surface attractive forces play a more decisive role in controlling the scattering dynamics at the OH-SAM. Beyond fundamental studies of energy transfer, this thesis provides detailed surface-science-based studies of the mechanisms involved in the uptake and decomposition of chemical warfare agent (CWA) simulants on or within metal-organic frameworks (MOFs). The work presented here represents the first such study reported in with traditional surface-science based methods have been applied to the study of MOF chemistry. The mechanism and kinetics of interactions between dimethyl methylphosphonate (DMMP) or dimethyl chlorophosphate (DMCP), key CWA simulants, and Zr6-based metal-organic frameworks (MOFs) have been investigated with in situ infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), and DFT calculations. DMMP and DMCP were found to adsorb molecularly (physisorption) to the MOFs through the formation of hydrogen bonds between the phosphoryl oxygen and the free hydroxyl groups associated with Zr6 nodes or dangling -COH groups on the surface of crystallites. Unlike UiO-66, the infrared spectra for UiO-67 and MOF-808, recorded during DMMP exposure, suggest that uptake occurs through both physisorption and chemisorption. The XPS spectra of MOF-808 zirconium 3d electrons reveal a charge redistribution following exposure to DMMP. Besides, the analysis of the phosphorus 2p electrons following exposure and thermal annealing to 600 K indicates that two types of stable phosphorus-containing species exist within the MOF. DFT calculations (performed by Professor Troya at Virginia Tech), were used to guide the IR band assignments and to help interpret the XPS features, suggest that uptake is driven by nucleophilic addition of a surface OH group to DMMP with subsequent elimination of a methoxy substituent to form strongly bound methyl methylphosphonic acid (MMPA). With similar IR features of MOF-808 upon DMCP exposure, the reaction pathway of DMCP in Zr6-MOFs may be similar to that for DMMP, but with the final product being methyl chlorophosphonic acid (elimination of the chlorine) or MMPA (elimination of a methoxy group). The rates of product formation upon DMMP exposure of the MOFs suggest that there are two distinct uptake processes. The rate constants for these processes were found to differ by approximately an order of magnitude. However, the rates of molecular uptake were found to be nearly identical to the rates of reaction, which strongly suggests that the reaction rates are diffusion limited. Overall, and perhaps most importantly, this research has demonstrated that the final products inhibit further reactions within the MOFs. The strongly bound products could not be thermally driven from the MOFs prior to the decomposition of the MOFs themselves. Therefore, new materials are needed before the ultimate goal of creating a catalyst for the air-based destruction of traditional chemical nerve agents is realized.
Doctor of Philosophy

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41

Dao, Tomáš. "Návrh nosné platformy pro nízkoteplotní UHV STM mikroskop". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231317.

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Diploma thesis deals with the design of a vibration isolated platform for low temperature scanning tunneling microscope working under ultra high vacuum (UHV STM). Cooling of the microscope is done by liquid helium using a flow cryostat designed in Institute of Scientific Instruments of the AS CR. In the thesis, general requirements of designing of an ultra high vacuum compatible devices are discussed, as well as the ways of vibrational isolation and damping. Also some ways how to restrict the transfer of vibration between vacuum devices and surroundings are mentioned. This knowledge is then applied to the design of the antivibrational microscope platform compatible with low temperature usage. For better understanding of vibrational transfer and damping, a real model of the designed platform is made and vibrational transfer characteristics are measured and compared with the theory.

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42

Höfer, Katharina [Verfasser], Liu Hao [Akademischer Betreuer] [Gutachter] Tjeng, Clemens [Gutachter] Laubschat i Kathrin [Gutachter] Dörr. "All in situ ultra-high vacuum study of Bi2Te3 topological insulator thin films / Katharina Höfer ; Gutachter: Liu Hao Tjeng, Clemens Laubschat, Kathrin Dörr ; Betreuer: Liu Hao Tjeng". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1129080935/34.

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Plogmaker, Stefan. "Techniques and Application of Electron Spectroscopy Based on Novel X-ray Sources". Doctoral thesis, Uppsala universitet, Yt- och gränsskiktsvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168799.

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The curiosity of researchers to find novel characteristics and properties of matter constantly pushes for the development of instrumentation based on X-radiation. I present in this thesis techniques for electron spectroscopy based on developments of X-ray sources both in time structure and energy. One part describes a laser driven High-Harmonic Generation source and the application of an off-plane grating monochromator with additional beamlines and spectrometers. In initial experiments, the source is capable of producing harmonics between the 13th and 23rd of the fundamental laser 800 nm wavelength. The intensity in the 19th harmonic, after monochromatization, was measured to be above 1.2·1010 photons/second with a repetition rate of 5 kHz. The development of a chopper system synchronized to the bunch clock of an electron storage ring is also presented. The system can be used to adjust the repetition rate of a synchrotron radiation beam to values between 10 and 120 kHz, or for the modulation of continuous sources. The application of the system to both time of flight spectroscopy and laser pump X-ray probe spectroscopy is shown. It was possible to measure triple ionization of Kr and in applied studies the valence band of a laser excited dye-sensitized solar cell interface. The combination of the latter technique with transient absorption measurements is proposed. The organic molecule maleic anhydride (MA) and its binding configuration to the three anatase TiO2 crystals (101), (100), (001) has been investigated by means of Xray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine structure Spectroscopy (NEXAFS). The results provide information on the binding configuration to the 101 crystal. High Kinetic Energy Photoelectron Spectroscopy was used to investigate multilayers of complexes of iron, ruthenium and osmium. The benefit of hard X-rays for ex-situ prepared samples is demonstrated together with the application of resonant valence band measurements to these molecules.

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Lu, Jessica Weidgin. "Dynamics of Atmospherically Important Triatomics in Collisions with Model Organic Surfaces". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77045.

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Detailed investigations of molecular collisions at the gas-surface interface provide insight into the dynamics and mechanisms of important interfacial reactions. A thorough understanding of the fundamental interactions between a gas and surface is crucial to the study of heterogeneous chemistry of atmospheric organic aerosols. In addition to changing the chemical and physical properties of the particle, reactions with oxidizing gases may alter aerosol optical properties, with implications for the regional radiation budget and climate. Molecular beams of CO₂, NO₂ and O₃ were scattered from long-chain methyl (CH₃-), hydroxyl (OH-), vinyl (H₂C=CH-) and perfluorinated (CF₃(CF₂)₈-, or F-) ω-functionalized alkanethiol self-assembled monolayers (SAMs) on gold, to explore the reaction dynamics of atmospherically important triatomics on proxies for organic aerosols. Energy exchange and thermal accommodation during the gas-surface collision, the first step of most interfacial reactions, was probed by time-of-flight techniques. The final energy distribution of the scattered molecules was measured under specular scattering conditions (θi = θf = 30°). Overall, extent of energy transfer and accommodation was found to depend on the terminal functional group of the SAM, incident energy of the triatomics, and gas-surface intermolecular forces. Reaction dynamics studies of O3 scattering from H2C=CH-SAMs revealed that oxidation of the double bond depend significantly on O₃ translational energy. Our results indicate that the room-temperature reaction follows the Langmuir-Hinshelwood mechanism, requiring accommodation prior to reaction. The measurements also show that the dynamics transition to a direct reaction for higher translational energies. Possible environmental impacts of heterogeneous reactions were probed by evaluating the change in the optical properties of laboratory-generated benzo[a]pyrene (BaP)-coated aerosols, after exposure to NO₃ and NO₂, at 532 nm and 355 nm by three aerosol analysis techniques: cavity ring-down aerosol spectroscopy (CRD-AS) at 355 nm and 532 nm, photoacoustic spectroscopy (PAS) at 532 nm, and an aerosol mass spectrometer (AMS). Heterogeneous reactions may lead to the nitration of organic-coated aerosols, which may account for atmospheric absorbance over urban areas. Developing a detailed understanding of heterogeneous reactions on atmospheric organic aerosols will help researchers to predict the fate, lifetime, and environmental impact of atmospherically important triatomics and the particles with which they collide.
Ph. D.

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Haque, Francia. "Réactivité de nanoparticules d'oxydes d'orientations définies". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066420/document.

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La connaissance d’un système gaz/solide requiert l’analyse de l’adsorption, du premier stade jusqu’à saturation. C’est la motivation de l’analyse des surfaces sous vide. L’approche des surfaces divisées est souvent tronquée. Pratiquée à des pressions suffisamment élevées pour être compatible avec un temps de réaction raisonnable, elle ne permet pas l'analyse de la surface nue à la monocouche. L’objectif du présent travail a été d’établir une continuité d’observation par FTIR, de l’UHV à la pression ambiante, de poudres de MgO, ZnO et ZnxMg1-xO exposées à l’eau ou à l’hydrogène. Il a été montré que les fumées de ZnO se comparent à des cristaux présentant les faces (0001), (0001̅), (101̅0), (112̅0), avec un rapport non-polaire/polaire de 75/25. Par FTIR combinée à la photoémission et à la désorption thermique, trois étapes de l’hydroxylation des fumées de MgO ont été identifiées : défauts ponctuels (10-8 mbar), marches (10-6 mbar) puis terrasses (> 10-5 mbar), avec une restructuration qui prouve que l’eau change la structure de surface de MgO. La représentation commune de la surface de MgO par une suite de facettes (100) est mise en cause. Aux faibles teneurs en zinc, l’oxyde mixte ZnxMg1-xO est formé de cristallites cubiques de même structure que MgO. Le zinc en substitution tend à ségréger vers les sites de basse coordinence où il affecte les propriétés d’adsorption d’eau et d’hydrogène. Par ailleurs, le mélange ZnO-MgO obtenu par combustion d’alliage ZnMg offre une possibilité d’application grâce aux propriétés bactéricides de ZnO et de faible toxicité de MgO. L’ensemble des résultats montre la pertinence de l’étude des poudres pratiquée dans les conditions de l’UHV
The analysis of adsorption from the first stage to saturation is necessary to understand gas/solid interactions. This is the motivation for surface analysis under vacuum. The common approach of dispersed materials surfaces is incomplete since working pressures, that are high enough to achieve reasonable reaction times, do not allow studies of powder surfaces from bare to fully covered. The aim of the present work is to examine the successive changes of ZnO, MgO and ZnxMg1-xO nanopowders upon exposure to water or hydrogen from UHV to the ambient by FTIR. It is shown that ZnO smokes behave in a same way as a collection of single crystals which exhibit (0001), (0001̅), (101̅0) and (112̅0) faces with a non-polar/polar ratio of 75/25. Combining FTIR with XPS and TPD techniques, three stages of hydroxylation were identified on MgO smokes: point defects (10-8 mbar), steps (10-6 mbar) then terraces (> 10-5 mbar). Results indicate a reorganisation of surface structure showing that water adsorption on MgO(100) is an irreversible process. The common model of MgO as a series of (100) facets is questioned. At low concentrations of zinc, the mixed oxide ZnxMg1-xO consists of crystals with similar structure as MgO. A segregation of Zn2+ toward low coordinated surface sites is suggested to explain the changes in reactivity of the ZnxMg1-xO with respect to water and hydrogen at low coverages. Furthermore, the mixture ZnO-MgO produced by combustion of ZnMg alloy combines the antibacterial properties of ZnO and the biocompatibility of MgO, interesting for potential applications. The overall results demonstrate the relevance of the study of powders in ultra-high vacuum conditions

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Deshpande, Aparna. "Atomistic interactions in STM atom manipulation". Ohio : Ohio University, 2007. http://www.ohiolink.edu/etd/view.cgi?ohiou169849272.

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Weiller, Sébastien. "Etude de la relation entre porosité et étanchéité à l'ultra-vide de dépôts à base d'aluminium obtenus par projection dynamique par gaz froid ("cold spray")". Thesis, Université Paris sciences et lettres, 2021. http://www.theses.fr/2021UPSLM004.

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La projection dynamique par gaz froid (« cold spray ») est un procédé de projection thermique dont l’un des atouts majeurs est de pouvoir conduire à des dépôts très denses. C’est cet atout qui sera prioritairement exploité dans cette étude pour la réalisation d’un revêtement métallique dont l’application lui requiert de présenter une haute étanchéité au gaz, dans des conditions de vide poussé. Le travail proposé porte sur la réalisation de ce type de revêtement dont il faudra étudier la porosité susceptible de se former à la projection. L’un des objectifs est de déterminer la taille critique de pore au-delà de laquelle le niveau d’étanchéité exigé n’est plus respecté ainsi que tous les autres critères de porosité susceptibles d’intervenir (répartition, géométrie, etc.). Plus fondamentalement, il s’agira d’associer, y compris à l’aide de la simulation numérique, ces caractéristiques aux mécanismes de formation des pores en fonction des conditions de projection. L’influence du substrat (métal ou polymère) sur la porosité, via les modifications dans le processus de construction du dépôt sera examinée. Son adhérence, au substrat sera aussi déterminée, sachant que la propriété première sur laquelle il convient de se pencher est l’étanchéité au gaz. Des mesures seront effectuées sur éprouvettes adaptées
Cold Spray is a thermal spray process, a key advantage of which is its capability to achieve highly-dense coatings. The practical objective of the study is to fully exploit this asset to obtain a metallic coating which exhibit gas-tightness in ultra-high vacuum conditions as requested for the targeted application. The thesis work consists in studying cold spray conditions to result in suitable properties. The study will focus on porosity formation mechanisms when spraying. A major objective is to determine a critical size for porosity above which gas-tightness no more meets the required specifications for the application. For this, relevant characteristics of pores (size, distribution, shape, ... ) will be assessed. More basically, the work aims to correlate, including using numerical simulation, these characteristics with the previously-mentioned formation mechanisms as a function of spraying conditions. The influence of the substrate (a metal or a polymer) onporosity will be studied in particular, through the study of modifications in the coating build-up. Coating-substrate bond strength will be determined, based on the study of adhesion mechanisms since an influence of these on gas-tightness can be expected

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Peyrot, David. "Engineering 2D organic nanoarchitectures on Au(111) by self-assembly and on-surface reactions". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX007/document.

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Ces dernières années ont été marquées par de grandes évolutions technologiques à travers notamment une course à la miniaturisation. De gros efforts de recherche se concentrent en particulier sur le domaine de l’électronique organique mais aussi sur de nouveaux matériaux bidimensionnels comme le graphène. Ces matériaux 2D présentent des propriétés physiques exceptionnelles et sont des candidats prometteurs pour le développement de futurs dispositifs électroniques. Au cours de cette thèse, l’approche ascendante, qui consiste à assembler ensemble des petites briques élémentaires, a été utilisée pour élaborer des nanostructures bidimensionnelles originales sur des surfaces. Des états électroniques localisés dus à un couplage électronique latéral particulier entre les molécules ont été observés. Quatre nanoarchitectures hybrides ioniques-organiques différentes ont été réalisées en faisant varier la température de la surface. Des nanostructures organiques covalentes ont aussi été élaborées par une réaction de couplage d’Ullmann sur la surface. Deux précurseurs différents en forme d’étoile avec des substituants iodés et bromés respectivement, ont été étudiés. De grandes nanostructures carbonées hexagonales poreuses ont notamment été synthétisées en faisant varier la température du substrat. Ces travaux ouvrent de nouvelles perspectives pour la réalisation de matériaux organiques bidimensionnels aux propriétés contrôlées
Over the last few years, important technological developments were made following a trend towards miniaturization. In particular, lots of research efforts are put into the research on organic electronics and on 2D materials like graphene. Such 2D materials show great physical properties and are promising candidates for the development of future electronic devices.In this project, bottom-up approach consisting in assembling elementary building blocks together, was used to engineer novel twodimensional nanostructures on metal surfaces. The properties of these two-dimensional nanostructures were investigated using Scanning Tunneling Microscopy (STM) and X-ray Photoemission Spectroscopy (XPS). Two-dimensional nanostructures based on the self-assembly of organic building blocks stabilized by intermolecular interactions were engineered. In particular, nanostructures stabilized by hydrogen bonds, halogen bonds and ionic-organic interactions were investigated. Localized electronic states due to specific molecular lateral electronic coupling were observed. Four different ionic-organic nanoarchitectures were engineered varying the substrate temperature. Covalent organic nanostructures were also engineered by onsurface Ullmann coupling reaction. Two different star-shaped precursors with iodine and bromine substituents respectively, were investigated. Large periodic porous 2D covalent hexagonal carbon nanostructures weresuccessfully engineered by temperature driven hierarchal Ullmann coupling. These results open new perspectives for the development of 2D organic materials with controlled structures and properties

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Lelaidier, Tony. "Organic semiconductor characterisation by scanning tunnelling microscopy and optical spectroscopy". Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4032/document.

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Les propriétés électroniques et d'autoassemblage de deux composés organiques, le DHTAP et le bis-pyrène, ont été étudiées par microscopie à effet tunnel (STM), sous ultra-vide et à basse température. Les propriétés optiques ont été étudiées par spectroscopie en cavité résonnante (CRD), également sous ultravide.La croissance du DHTAP a été étudiée sur différents métaux nobles. La croissance du bis-pyrène a été étudiée sur Au(111). Dans chaque cas, les conditions de température idéales pour la formation d’une première couche organisée ont été déterminées. Différents modèles sont proposés pour les structures observées en première couche. La formation de la seconde couche moléculaire à également été étudiée.L'évolution des propriétés optiques, étudié par CRD, du bis-pyrène déposé sur du verre borosilicate combinée aux informations obtenues par STM ont permit d’associer ces modifications aux interactions des moments dipolaires de transition des molécules de la première et de la seconde couche et on également permit de déterminer le mode de croissance.Finalement, la possibilité d’induire des modifications chimique de la molécule de DHTAP, intégrée dans une couche auto-assemblée, en utilisant le courant tunnel du STM a été observé. Il s’avère que la molécule de DHTAP intégrée en première couche peut subir une double déshydrogénation pour conduire à la formation d’un composé identifié comme étant le 5,7,12,14-tetraazapentacene (TAP). En seconde couche, la formation de deux radicaux, en plus du TAP, a été observé. La molécule de TAP présente un certain intérêt du fait qu’elle n’est pas synthétisable pas les méthodes conventionnelle de chimie organique
Electronic and self-assembling properties of two organic compound, the DHTAP and the bis-pyrene, have been studied by the means of low temperature scanning tunnelling microscopy (STM) under ultrahigh vacuum conditions. Optical properties have been studied by cavity ring-down (CRD) spectroscopy, also under ultrahigh vacuum conditions.The growth of DHTAP has been studied on different metallic substrate. The growth of bis-pyrene has been studied on Au(111). In each case, the optimal temperature conditions for the formation of a well-ordered first monolayer have been determined. The formation of second monolayers has also been studied. The evolution of the optical properties, studied by CRD, of bis-pyrene deposited on borosilicate glass combined with information obtained from STM allow us to identify these modifications as interactions between transition dipole moments of molecules in the first and in the second layer, and also determine the growth mode.Finally, the possibility to induce chemical modification of DHTAP molecules embedded in an ordered monolayer using the tunnelling current of the STM has been studied. It appears that the molecule embedded in the first ML can be doubly dehydrogenated which leads to the formation of a compound identified as 5,7,12,14-tetraazapentacene (TAP). In the second layer, the formation of two radicals in addition to the TAP has been observed. The TAP molecule is interesting because of that it cannot be synthesized using common organic chemical methods

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Sordes, Delphine. "Imagerie, manipulation et contact électronique atome par atome sur la surface Si(100) : H avec le microscope à effet tunnel basse température à 4 pointes". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30048/document.

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La construction de circuits électroniques de section atomique est l'un des grands défis de la nanoélectronique ultime. Pour construire un circuit électronique atomique, il faut d'abord mettre au point l'instrument de construction puis choisir la surface-support stabilisant ce circuit. Sur la surface d'Au(111) préparée en ultra vide, nous avons mis en œuvre et stabilisé le tout premier LT-UHV-4 STM. Ce microscope à 4 pointes STM balayant en même temps et indépendamment une même surface a été construit pour le CEMES par la société ScientaOmicron. Sur l'Au(111), nous avons reproduit tous les résultats expérimentaux obtenus sur les meilleurs LT-UHV-STM à une pointe comme la précision en rugosité de 2 pm, les caractéristiques I-V sans moyenne sur un seul atome pendant plusieurs dizaines de minutes et la manipulation atomique suivant les modes de tiré, glissé et poussé d'un seul atome d'or sur la surface. Une fois cette optimisation réalisée, nous avons appliqué notre LT-UHV-4 STM à la surface de Si(100):H, support probable des futurs circuits atomiques électroniques. Le choix de ce support est discuté en détail avant l'enregistrement et l'analyse des images STM. Les échantillons utilisés proviennent, soit du procédé semi-industriel pleine-plaque de silicium mis au point au CEA-LETI, soit de leur préparation in situ se déroulant directement dans la chambre de préparation du LT-UHV-4 STM. Nous avons pris soin de bien interpréter les images STM de la surface Si(100):H afin par exemple de déterminer la position de chaque atome d'hydrogène. La lithographie atomique par STM a été exploitée, par pointe, sur le LT-UHV-4 STM, en mode manipulation verticale atome-par-atome et mode balayage plus rapide mais rendant l'écriture atomique moins précise. Nous avons construit nos propres fils atomiques puis des plots de contact atomiques, petits carrés de Si(100)H dépassivés de quelques nm de côté. Les courants de fuite à 2 pointes et à l'échelle atomique ont ainsi pu être mesurés sur la surface de Si(100):H entre deux de ces plots. Pour préparer les contacts atomiques à au moins 2 pointes sur un fil atomique ou sur des plots de contact nanométrique, nous avons étudié en détail les différents types de contact pointe STM-liaison pendante unique montrant la difficulté d'atteindre un quantum de conductance au contact, de par un effet de courbure de bandes. Il est donc difficile sans une mesure de force complémentaire de déterminer en partant du contact tunnel les différentes étapes du contact mécanique, électronique au contact chimique. Nos résultats ouvrent la voie à la caractérisation des circuits électroniques construits atome par atome et à l'échelle atomique à la surface d'un semi-conducteur
The construction of electronic circuits of atomic section is one of the great challenges of the ultimate nanoelectronics. To build an atomic electronic circuit, it is necessary first to develop the dedicated instrument to build up and then to choose the support surface stabilizing this circuit. On the Au(111) surface prepared in ultra-vacuum, we implemented and stabilized the very first LT-UHV-4 STM. This STM 4-probes microscopes scanning at the same time and independently the same surface was built for the CEMES by the ScientaOmicron company. On Au(111), we reproduced all the experimental results obtained on the best LT-UHV-STM with one probe such as the precision in roughness of 2 pm, the IV characteristics recording without any average on a single atom for several tens of minutes and the atomic manipulation following the pulling, sliding and pushing modes of a single gold atom on the surface. Once this optimization was carried out, we applied our LT-UHV-4 STM to the surface of Si(100):H, probable support of the future electronic atomic circuits. The choice of this medium is discussed in detail before recording and analysis of the STM images. The samples used come either from the semi-industrial full-wafer silicon process developed at CEA-LETI or from their in-situ preparation, which takes place directly in the preparation chamber of the LT-UHV-4 STM. We have taken care to interpret the STM images of the surface Si(100):H in order to locate the position of each hydrogen atom. The atomic lithography by STM has been exploited, by using one tip from our LT-UHV-4 STM, by atom-per-atom vertical mode and faster scanning mode. The last makes atomic writing less accurate. We have constructed our own atomic wires and then atomic contact pads, small squares of Si(100)H defeated by a few nm sides. The leakage currents with 2 probes at the atomic scale have thus been able to be measured on the surface of Si(100):H between two of these pads. To prepare the atomic contacts at least 2 probes on an atomic wire or on nanometric contact pads, we studied in detail the different types of contact points STM-single dangling bond showing the difficulty of reaching a quantum of conductance at contact, due to a possible bands bending. It is therefore difficult without a complementary force measurement to determine, starting from the tunnel contact, the different steps of the mechanical, electronic contact at the chemical contact. Our results open the way to the characterization of electronic circuits constructed atom-by-atom and at atomic scale on the surface of a semiconductor

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